1. Field of the Invention
The present invention relates to a high-temperature gas control valve for controlling a flow of a high-temperature gas to be used in semiconductor manufacturing equipment or process.
2. Description of Related Art
In semiconductor manufacturing equipment, a high-temperature process gas is delivered to a chamber via a gas control valve controlled to open/close for regulating a flow of the gas. As such the gas control valve, generally used is a diaphragm valve in order to prevent the gas from remaining therein. In this diaphragm valve, a metal diaphragm is usually used in consideration of a problem that a diaphragm made of resin (e.g., polyimide resin) may allow gas to permeate therethrough.
Accordingly, a valve section of the gas control valve is constructed of a combination of a metal diaphragm made of stainless steel and a valve seat made of resin.
In recent years, however, the temperature of gas to be used in the semiconductor manufacturing process has been increased up to 300xc2x0 C. In association with this, the resinous valve seat could not provide sufficient durability compared with the metal diaphragm. The resinous valve seat is produced as a standard product. On the other hand, there is used a gas control valve provided with a valve seat made of metal such as stainless steel and the like, instead of resin. This metal valve seat forms a metal seal with respect to the metal diaphragm in the gas control valve.
However, the gas control valve in which the metal seal is made has a problem of an extremely short life.
Hence, a leakage test for examining durability was made on the conventional gas control valve in a case of controlling a normal-temperature (23xc2x0 C.) gas and in another case of controlling a high-temperature (300xc2x0 C.) gas. Test results thereof are shown in FIG. 3. FIG. 3 is a graph showing the amount of leaked gas with respect to the number of operations of repeatedly opening and closing the gas control valve in each case. In this graph, a line S1 denotes a result obtained in the case of regulating the normal-temp. gas. S2 denotes another result obtained in the other case of regulating the high-temp. gas. It is to be noted that a line S3 is a test result obtained about the apparatus of the present invention (mentioned later) when operated for the high-temp. gas. A reference value E indicates an upper limit of leakage standards. As a result of this leakage test, as seen from the graph, in the case of the normal-temp. gas (S1), the amount of leakage was substantially unchanged throughout the operations and the valve could maintain its initial sealing capability even after one hundred thousand operations. On the other hand, in the case of the high-temp. gas (S2), the amount of leakage exceeded the reference value E after several tens of operations.
Sealing portions of the diaphragm and the valve seat after the above durability test are shown in plan views in FIGS. 6 and 7. FIGS. 6A and 6B are diagrams illustrating microscope photographs (FIGS. 9A and 9B) of parts of annular sealing portions, namely, contact surfaces of the diaphragm and the valve seat, respectively, of the valve which was operated to open and close one hundred thousand times to control the normal-temp. gas (23xc2x0 C.). FIGS. 7A and 7B are diagrams illustrating microscope photographs (FIGS. 10A and 10B) of parts of annular sealing portions, namely, contact surfaces of the diaphragm and the valve seat, respectively, of the valve which was operated to open and close ten thousand times to control the high-temp. gas (300xc2x0 C.).
From the durability test, it was confirmed the reason why the sealing portions of the diaphragm and the valve seat caused gas leakage. That is, comparing FIGS. 6A and 6B and FIGS. 7A and 7B, it is found that the sealing portions of the gas control valve for the high-temp. gas (FIGS. 7A and 7B) had many linear large scratches extending in the direction of the radius of the sealing portions (in an up-and-down direction in the figures), for example, at the portion indicated by an arrow P. Such the scratches were not generated in the valve for the normal-temp. gas (FIGS. 6A and 6B).
On the other hand, in the sealing portions of the valve for the normal-temp. gas shown in FIGS. 6A and 6B, scratches were generated along the annular sealing portions, for example, at a portion indicated by an arrow Q, by the contact between the diaphragm and the valve seat. However, no scratches which might cause the gas leakage were generated even after one hundred thousand opening and closing operations.
The linear scratches P shown in FIGS. 7A and 7B, which were produced in the sealing portions in the case of the high-temp. gas, appear on both the diaphragm and the valve seat. Thus, it is likely that those scratches produce cracks which provide communication between a primary side (the inside of the valve seat 26, namely, the passage leading to the input port 27) and a secondary side (the outside of the valve seat 26, namely, the passage leading to the output port 28) of the sealing portions in a valve closed state, causing the leakage of gas through the sealing portions.
The above conventional gas control valve also has a problem that rubbing of the diaphragm and the valve seat produces a large amount of dusts, forming particles which reduce yields of the semiconductor manufacture.
Therefore, it is urgently necessary in the semiconductor manufacture field to develop a gas control valve adaptable for a high-temp. process gas.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a high-temperature gas control valve with high durability, capable of controlling the flow of a high-temperature gas.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a high-temperature gas control valve for controlling a flow of a high-temperature gas, including: a valve seat made of metal; a diaphragm made of metal, which is brought into contact with or separated from the valve seat by operation of an actuator, thereby opening and closing the valve; wherein at least one of the diaphragm and the valve seat is coated with an amorphous-carbon film.
According to the present invention, the amorphous carbon film is formed on at least one of the diaphragm and the valve seat. The diaphragm and the valve seat with an amorphous structure can have a low coefficient of friction and the excellent resistance to adhesion. This can achieve a high-temp. gas control valve for controlling a flow of a high-temp. gas, which can perform opening-and-closing operations a sufficient number of times without causing gas leakage, and also minimize the generation of particles.